Process for improving an electrode

Abstract

A process for increasing the active surface area of at least one electrode having a surface comprising a group VIII metal in an electrochemical cell, which also comprises at least one balancing electrode and an aqueous electrolyte which comprises nitrate ions, which comprises applying a sweeping voltage across the electrodes at a rate of at least 0.2 V/s, the sweeping voltage being from a lower voltage which is between the voltage at which hydrogen evolution occurs and −0.7 V to an upper voltage which is between −0.2 V and +0.3 V, all of the above voltages being with reference to a standard calomel reference electrode (VSCE).

1. A process for increasing the active surface area of at least one electrode, acting as a cathode, having a surface comprising rhodium in an electrochemical cell, which also comprises at least one balancing electrode and an aqueous alkaline electrolyte which comprises nitrate ions and halide ions; which comprises applying a sweeping voltage across the electrodes at a rate of at least 0.2 V/s, the sweeping voltage being from a lower voltage which is between the voltage at which hydrogen evolution occurs and −0.7 V to an upper voltage which is between −0.2 V and +0.3 V, all of the above voltages being with reference to a standard calomel reference electrode (V SCE ), wherein the activated electrode converts nitrate ions in the electrolyte solution to nitrogen gas and wherein the sweeping voltage is applied either continuously or at a rate of from 1 to 10 sweep cycles even 10 seconds to 5 minutes to maintain the activity of the activated electrode. 
     
     
       2. A process according to  claim 1  wherein the electrochemical cell is operated at a temperature of from 50 to 70° C. 
     
     
       3. A process according to  claim 1  wherein the sweeping rate is up to 0.8 V/s. 
     
     
       4. A process according to  claim 1  wherein the halide ion is chloride. 
     
     
       5. A process according to  claim 1  wherein the electrolyte comprises chloride ions and hydroxide ions. 
     
     
       6. A process according to  claim 5  wherein the electrolyte comprises up to 3 M chloride ions and up to 1 M hydroxide ions. 
     
     
       7. A process according to  claim 6  wherein the electrolyte comprises approximately 2M chloride ions, approximately 0.5M hydroxide ions, and approximately 0.2M nitrate ions. 
     
     
       8. A process according to  claim 5  wherein after a period of from 5 to 7 days the hydroxide molarity in the electrolyte is reduced to approximately 0.2M. 
     
     
       9. A process according to  claim 1  wherein the electrolyte comprises up to 0.5 M nitrate ions. 
     
     
       10. A process according to  claim 1  wherein said sweeping voltage is applied for a period of at least five days to initially activate the electrode. 
     
     
       11. A process according to  claim 1  wherein approximately 6 complete voltage cycles are applied every approximately 3 minutes. 
     
     
       12. A process according to  claim 1  wherein the active surface area of the electrode having a surface comprising rhodium is increased to at least 7 times the surface area of the electrode prior to being treated. 
     
     
       13. A process according to  claim 1  wherein the activated electrode is used in the electrolysis of aqueous solutions to remove dissolved nitrate tons. 
     
     
       14. A process according to  claim 1  wherein said process produces an electrode surface with reduced actiation energy required for the conversion of nitrate ions in aqueous solution to nitrogen gas.